Particles in fluids can be quantified in a number of ways. The number of particles present in an oil sample from a motor or engine greater than a certain size, for example, can be indicative of the condition of certain motor or engine components and/or indicative of impending failure.
Traditionally, ferrography analysis using optical microscopy is used to determine abnormal failure modes in machines based on visual inspection of large particles and their associated morphologies. This type of analysis can be time consuming and subjective because it requires an expert analyst. More recent direct imagining instruments have been developed to automatically quantify the size and distribution of wear particles and to also provide some indication of shape. One limitation of such devices is their inability to analyze highly viscous oils and very dark fluids without dilution. The resulting particle counts can often be skewed because of interference from additives, water, and dissolved gases.
U.S. Pat. No. 4,583,396, incorporated herein by this reference, teaches a by-pass contamination indicator for a hydraulic system. The system includes a barrier which, when blocked by particles, causes a pressure drop across the barrier to reach a certain value. By counting how long it takes to reach this pressure value, the general contaminate level (low, medium, high) can be determined. The total number of particles larger than the barrier pore size is said to be calculated based on the pore size, the number of pores, the flow rate, and pressure drop.
This system is adapted for addition to a hydraulic system; not for analyzing samples of fluid. Moreover, the emphasis of such a system is cleanliness control and keeping such a system clean and free of contamination to known limits is the primary goal. In a hydraulic system, the valves and actuators must be kept clean and free of debris to function properly. Light blocking and pore blockage technology has been designed around such clean systems.
In lubrication systems, benign wear particles are generated as a natural consequence of the mechanical operation of the machine being lubricated. A good example is a diesel engine. The extremities of the components in the cylinder and the piston acting between a hydrodynamic film of lubricant act as a stable wearing surface and particles are exfoliated as normal rubbing wear platelets. Existing light blocking and pore blockage technologies are not ideally suited for these applications without some degree of sample preparation.